Bonjour is a zero configuration network multicast Domain Naming System protocol used by devices developed by Apple Inc. to enable the automatic and easy discovery of computers, devices, and services on Internet Protocol (IP) networks. Bonjour (like other multicast services, such as Microsoft's UPnP) uses industry standard IP protocols to allow devices to automatically discover each other without the need to enter IP addresses or configure DNS servers. This brings simplicity and ease-of-use to the users of network devices and services. Eliminating the need to set up services such as Dynamic Host Configuration Protocol, DNS, and DNS Service Directory, Bonjour enables each device to continuously publish and discover services. By broadcasting Bonjour service messages, printers, servers, and other shared devices can advertise the services they offer. Client devices then monitor Bonjour advertisements and connect to the appropriate servers, as with any other service. The protocol also allows for a device to request services (Service Discovery) on the network as well as respond to incoming requests. A single device can be both a client and a server at the same time. The automatic discovery makes it easy for clients to easily use services offered by another device or server.
On the downside, Bonjour generates a lot of network traffic. During the Service Discovery process, when a device is browsing for services, it sends queries to discover whether a particular service is available in a network or in a domain. It issues an initial query and then sends subsequent queries exponentially less often, after 1 second, 2 seconds, 4 seconds, 8 seconds, and so on, at up to a maximum interval of one hour. Likewise, when a service starts up on the network, it announces its presence with the same exponential back-off algorithm. In a network that are connected through public networks, private networks, tunnels, or virtual private networks (VPN) the amount of such traffic can be substantial. With hundreds or thousands of Apple clients on a network, multicast traffic quickly swells to startling percentages.
The other problem with Bonjour (and similar multicast services) is that the broadcast of service advertisements are only seen by devices within a single subnet or Virtual Local Area Network (VLAN). Therefore in an enterprise with a large multi-VLAN network, the Bonjour traffic will not span across VLANs. This means Bonjour devices like printers in one VLAN cannot be used by client device in another VLAN.
As a result, when two networks are connected together or when one host is connected to another network through IP based tunnel, multicast data, such as data from Bonjour Protocol, are usually blocked in order to reduce network traffic. The blocking of this multicast data creates inconvenience to users and hosts as users and hosts are unable to receive multicast data originated from another network.
Internet Engineering Task Force (IETF) Request For Comments (RFC) 6513 has disclosed a method to relay IP based multicast data to different networks through tunnels and/or MPLS technologies. IETF RFC 6513 specifies special protocols and procedures how multicast traffic within a BGP/MPLS IP VPN travels from one VPN site to another.
Cisco has disclosed a Bonjour Gateway, by caching Bonjour advertisements from one or more source/host and responding back to Bonjour clients when the Bonjour clients ask for or request a service. The solution disclosed by Cisco requires the Bonjour Gateway to understand Bonjour protocol in order to cache Bonjour traffic and make request or reply on behalf of other Bonjour protocol capable devices. The Bonjour Gateway acts like a proxy.
Another method is to use specifically configured DNS server to provide IP based multicast data to different networks. However, not all networks are allowed to have specifically configured DNS server.
If the multicast data-link layer data is non-discriminatorily being transmitted, routed or forwarded from one network to another network, the capacity of the tunnel may be consumed by the multicast data-link layer data. Therefore, intelligent methods are required to be implemented at the gateway or router in order to allow multicast data being transmitted, routed or forwarded discriminatorily while not consuming too much network resources.